Conversion of hydrocarbon oils



May 20, 1941. P. MATHER CONVERSION 0F HYDROCARBON OILS Filed Oct. 20. 19.38

Patented May 20, 1941 2,242,255 CONVERSION OF HYDRO'CARBON OILS Percy Mather, Chicago, Ill., assignor to Universal -Oil Products Company, Chicago, Ill., a corporation of Delaware Application october 20, 193s, Serin No. 235,938

8 Claims.

The invention particularly refers to a novel and advantageous process for the extensive distillation and reduction of residual liquids resulting from the pyrolytic conversion of hydrocarbon oils to a heavier residual product, accompanied by the i, production from said cracked residue of high yields of lighter and more desirable oil suitable, for example, as premium fuel.

While the features of the invention are applicable to the treatment of practically any heavy E residual oil, they are particularly advantageous as applied to the treatment of residual oils resulting from cracking and the residuum distilling and reducing system may be operated in conjunction with practically any type of cracking unit ,n

wherein heavy liquid residue is produced.

From the following more detailed description of the process, its advantages will be readily apparent to those familiar with the art. It offers a means of recovering high yields of more valuable products from cracked residues without resorting to coking and without the deleterious degree of destructive distillation which is common to coking operations and results in high gas losses and reduced yields of valuable light liquid products.

cur and the resulting highly heated products are K quickly separated at sub-atmospheric pressure and/or in the presence of light vapors which exert a partial pressure effect, leaving a final residual product which is normally solid or semisolid at atmospheric conditions but which, due to the high temperature prevailing in the last mentioned vaporizing and separating step, may be quickly and continuously removed therefrom in liquid state and recovered. Preferably, the vaporous products evolved from the cracked residue in both the primary and secondary flashing steps or, more particularly, the components of these vapors which boil above therange of the desired final light distillate (gasoline) product of the process, are condensed and returned to the cracking system wherein said liquid residue is produced or to a separate cracking system for further cracking treatment, to produce therefrom additional yields of valuable light distillate such as gasoline. The vapors evolved in the cracking and reduced pressure vaporizing` step, to which the flashed residue is supplied, are condensed and recovered as a final product of the process and, due to the treatment afforded the flashed residue in accordance with the provisions of the invention, the yields of this product will often exceed 50% by weight of the fiashed residue. It Will consist essentially of an oil of materially lower boiling characteristics than the flashed residue and its characteristics may be controlled to meet market requirements for premium fuel oil.

The accompanying diagrammatic drawing illustrates one specific form of apparatus embodying the features of the invention and lin Which the process of the invention may be conducted. In this illustration, the residue-reducing steps are interconnected and conjointly operated with a relatively simple form of single coil cracking system, but it will be evident, as previously stated, that the novel features provided by the invention may be advantageously employed in conjunction with other types and other specific forms of cracking systems.

Referring to the drawing, heating coil l is disposed Within a furnace 2 and the oil supplied to this coil, in the manner which will be later described, is heated therein to the desired cracking temperature, preferably at a substantial superatmospheric pressure by means of heat derived from the furnace. The resulting heated products are discharged from coil I through line 3 and valve 4 into reaction chamber 5 wherein their cracking treatment continues at a superatmospheric pressure which may be substantially the same or somewhat lower than that employed at the outlet of coil I, chamber 5 being preferably insulated to conserve heat, although insulation is not indicated in the drawing.

Both vaporous and liquid conversion products are withdrawn, in the case here illustrated, from the lower portion of chamber 5 in commingled state and are directed through line 6 and valve 'l to vaporizing and separating chamber 8 which comprises the first flash distilling zone of the system and is operated at a substantially reduced pressure relative to that employed in chamber 5.

Thev vapors evolved from the liquid conversion products in chamber 8 and the vaporous products supplied to this zone from chamber 5 are directed from the upper portion of chamber 8 through line 8 and valve l0 to fractionation in fractionator Il.

In fractionator Il, the components of the vaporous products supplied to this zone which boil above the range of the desired final light distillate products of the process are condensed therein as reiiux condensate. In this particular case, the total reflux condensate formed in fractionator II, with the exception of a relatively small amount of selected low-boiling fractions which are separately removed therefrom and utilized, as will be later described, is directed from the lower portion of the fractionator through line I2 and valve I3 to pump I4 by means of which it is supplied through line I6 and valve I1 to cracking treatment, as previously described, in heating coil I. It is, however, entirely within the scope of the invention to employ a cracking` system utilizing a plurality of heating coils and, in such cases, the reflux condensate may, when desired, be separated by its fractional condensasation in fractionator II into selected relatively low-boiling and high-boiling fractions which are subjected in separate heating coils ofthe system to independently controlled cracking conditions. Fractionated vapors of the desired end-boiling point and consisting, in this particular case, ol vapors boiling Within the range of the desired gasoline product and gases, are directed from the upper portion of fractionator II through line I8 and valve I9 to condenser 2) wherein they are subjected to condensation andv cooling; The resulting distillate and uncondensed` gases are directed from condenser 28 through line 2I and valve 22 to collection and separation in receiver 23. The gases which remain uncondensed and undissolved in the distillate in receiver 23 are released therefrom through line 24 and valve 25 to storage or elsewhere, as desired'. Distillate collected in receiver 23is withdrawn therefrom through line 25 and valve 21 to storage or to any desired further treatment. Regulated quantities oi the distillate collected in receiver 2'3 may, when desired, be returned by means of line 28, valve 29, pump 3B, line 3l andvalve 32 to the upper portion of fractionator I I to serve as areuxing and cooling medium in this Zone.

The liquid residue resulting from flash distillation of the liquid conversion products in chamber 8 is withdrawn from the lower portion of this zone through line 33 and a regulated portion thereof may, when desired, be directed to cooling and storage through line 3-'1 and valve 35 and recovered as a final product of the process. However, at least a substantial portion of this flashed residue is directed through valve 36 in line 33 to a secondary vaporizing or ash distilling chamber 31 which is operated at a` substantially reduced pressure relative to that employed in chamber 8 and wherein the primary flashed residue is substantially further vaporized.

The vapors which are evolved and remain uncondensed in chamber 31 aredirected from the upper portion of this zone through line 38 and valve 39 to dephlegmator 40 wherein a rough separation of their relatively light andrelatively heavy components is accomplished. by fractional condensation. Dephlegmator 40 also serves in this particular case as a Zone to which hydrocarbon oil charging stock for the processis supplied and wherein it is preheated by direct contact with the relatively hot vapors from chamber 31 and serves as a refluxing and coolingr me- F dium for the vapors. The charging stock, which is preferably an oil of high-boiling characteristics or relatively wide boiling range, although it may be any desired type of oil, is supplied through line 4I and valve 42 to pump 43 by means of which it is 'fed through line 44 and valve 45 into dephlegmator 40.

The relatively heavy components of the vapors supplied to dephlegmator 4G which are condensed as reux condensate in this zone and the preheated charging s-tock, or the components thereof which remain unvaporized in dephlegmator 40, are directed from the lower portion of this zone. through line 46 and valve 41'to pump 48 by means of which this material is supplied through line 49, valve 50, line 5I and valve 52 to fractionator II. The oil thus supplied from dephlegmator 40 to fractionator II is directly commingled inthe latter zone with the relatively hot vapors, undergoing fractionation therein, serves as a cooling and refluxing medium for assisting fractionation of the vapors and the components of this oil which remain unvaporized in fractionator I I commingle with the reflux condensate formed therein and are directed therewith, in the manner previously described, to cracking treatmentin heating coil I. This oil may contain an appreciable quantity of components boiling within the range of the desired lightdistillate product of the process. In such cases, these desirable low-boiling components will be included with the stream of fractionated vapors removed from the upper portion of fractionator II and will be recovered with the rest of the,` light distillate product in receiver 23.

When, the oil withdrawn from the lower portion of dephlegmator 40 and/or the reflux condensate formed in this zone contains any substantial quantity of low-boiling fractions, which are undesired as components of theI final light distillate product'l collected in receiver 23, this oil instead of'being supplied to fractionator II, as illustrated, may be supplied by well known means, notshoWn, directly to coil I or to a separate cracking coil ofthe system, in case a multiple coil cracking system is employed.

The low-boiling components of the vapors from chamber 31; whichremain uncondensed in dephlegmator 40, and the low-boiling components ofthe charging stock supplied to this zone, which are vaporized and are not recondensed therein, are directed from the upper portion of the dephlegmator through line 53 and valve 54 to condensation and cooling in condenser 55 wherefrom the resulting distillate and any uncondensed gases are directed through line 56and valve 51 to collection and separation in receiver 58.

The gases which. remain uncondensedand un- `dissolved in the distillate collected in receiver 58 are released from this zone through. line 59 and valve 50 to storage or elsewhere, as desired. All or a portion ofthe distillate collected in receiver 58 may.,` when desired, be recovered as` a final product of the process,` by Well known means not illustrated, or it may be directed all or in part, from receiver 58 through line 6I and valve 52 to. pump S3by'means of whichv it is fed through line 64 Wherefrom it may be supplied, all or in part, through lineES, valve 66, line 5I and' valve 52y to fractionator III, to serve as a cooling and refluxing medium in this zone and therein undergo the same fractionating, treatment afforded the other materials supplied thereto. Also, regulated" quantities of. the distillate collected' in `receiver 58 may, When desired, be returnedthrough valve B1 in line 64 to the upper portion of chamber 31 tol comming-le therein with the` vapors evolvedin this zone. and serve-as a cooling and refluxing medium thereby assisting the desired separation ofvapors and non-vaporous residue in this zone. l Y

The invention also contemplates the use of a cooling and reuxing medium in the upper portion of chamber 8 to assist the desired separation of vapors and non-vaporous residue invthis zone.- Line 68 and valve I'69 is provided for the Vpurpose of introducing a cooling oil into the upper portion of chamber 8 and this material may comprise, for example, regulated'quantities of the distillate collected in receiver 58 -or regulated quantities of all or selected fractions of the condensate formed in fractionator II orlin dephlegmator 48, although well known means for supplying any of these variousfmaterials or any combination thereof toline 68 are omitted from the drawing for the sake of eliminating details lwhich will be readily apparent withoutillustration.

When the charging. stock supplied to dephlegmator 48 contains low-boiling fractions undesired as components of the light distillate product collected in receiver 23, such as, for example, gasoline or gasoline fractions of inferior antiknock value, fractionation of the charging stock is preferably so controlled in dephlegmator 40 that substantially all of these undesired low-boiling fractions are included in the overhead vaporous stream removed from this zone. In such cases the distillate collected in receiver 58 is preferably not supplied to fractionator II, but may be supplied, when desired, by well known means not illustrated, directly to coil I or to a separate cracking coil of the system, in case a multiple coil cracking system is employed.

Due to the extensive Vaporization afforded the vcracked residue in chambers 8 and 31, the heavy residual liquid product which remains unvaporized in the latter zoneV will be substantially free of low-boiling components desirable as cracking f Vstock for heating coil I and, except for the advantageous further treatment to which this material is'subjected, in accordance with theprovisions of the invention, it would ordinarily be suitable only as coking stock for producing high yields of coke, minor yields of lower boiling liq- .uid products and substantial quantities of gas. ,In accordance with the features ofthe invention, however, this heavy flashed residue is subjected to controlled further cracking treatment and .thereby converted into major yields of lighter and more valuable liquid, minor yields of a pitchylike or semi-solid residue, low yields of gas and no substantial quantity of coke. To accomplish this, the heavy flashed residue is directed from the lower portion of chamber 31 through line 10 vand valve 1I to pump 12 by means of which it is fed through line 13, valve 14 and line 15 to heating coil 16.

Coil 16 is located 'within a furnace 11 and, although illustrated in a conventional manner in the drawing, coil 16 and furnace 11 preferably comprise one of several well known types of heaters employing relatively high rates of heating and high oil velocities through the coil,

so that the flashed residue may be quickly heated to the desired cracking temperature in coil 16 and discharged therefrom through line 18 and valve 19 into chamber 80 before deleterious secondary cracking reactions, which result in the vformation of coke and excessive yields of gas, can occur. y

' Preferably, in order to increase the velocity of .flow through coil 16 and decrease the time during` which the flashed residue is maintained atan active cracking temperature in this zone, a

ly termed pressure distillate bottoms.

regulated. quantity of relatively light distillate is supplied to this zone with the flashed residue. 'I'his light `distillate is preferably an oil which is not readily cracked to produce coke and gas andA may be derived from any external source or from within the system. In the particular case here illustrated, the low-boiling oil supplied to coil 16 comprises a selected low-boiling fraction of the reux -condensate formed in fractionator II and consisting essentially of what is common- This material is removed as a si-destream from the upper portion of fractionator I I and vdirected through line 8l, valve 82, and pump 83 by means of which it is supplied through line 84, valve 85 and line 15 to the inlet of heating coil 16.

When light distillate is supplied, as previously described, -to coil 16, its substantially complete vaporization in chamber will exert a partial pressure effect on the products of the flashed residue cracking operation which would otherwise remain unvaporized in this zone. The invention also contemplates the use of sub-atmospheric pressure, when desired, in chamber 88 to assist vaporiza-tion and prevent substantial cracking therein. Due to the low eiective pressure maintained in chamber 88, cracking of the flashed residue supplied to coil 18 will be substantially limited to that which takes place in the lat-ter zone and may be quite accurately regulated by proper design of the heater for the capacity desired and by control of the rates of heating and oil velocity in the coil. By proper regulation of the control factors mentioned, the flashed residue may be cracked to su-ch a degree in coil 18 and the products vaporized to such a degree in chamber 80 that high yields of lighter and more valuable liquid products are produced without excessive gas formation and `without the production of any substantial quantity of coke, leaving a nonvaporous residue which, although normally solid or semi-solid under atmospheric conditions, may be continuously and quickly removed in liquid state from chamber due to the temperature prevailing in this zone. This product is preferably withdrawn from the lower portion of chamber 88 without permitting any substantial body thereof to accumulate in this zone and is directed through line 86 and valve 81 to pump 88 by means of which it is discharged from 4the system to cooling and storage or elsewhere, as desired, through line 88 and Ivalve 90. l u

Since chamber 88 functions as a zone wherein a high degree of vaporization is required and since for best results substantially all of the evolved vapors should be separated from the non-vaporous residue in this zone and separately removed therefrom, it is highly desirable to avoid any substantial cooling and fractionation of the evolved vapors in chamber 80, since this would result in appreciable recondensation of the vapors and blending of the resulting condensate withthe non-vaporous residue, thus including in the latter relatively low-boiling fractions which are more desirable as components of the overhead condensate. In view of this, I preferably avoid the use of a cooling and reuxing medium in the upper portion of chamber 80. However, the vapors evolved in this zone will `ordinarily contain appreciable quantities of entrained or dissolved heavy tar-like and pitchy materials which would bey deleterious as components of the nal fuel oil product and for best. results must be excluded from the overhead A'stream of vapors removed from the chamber 80.

To accomplish the separation ofsuch deleterious materials from the: relatively clean vapors, I pref'- erably providesuitable and well known contact.- ing means such as bafiles, perforated pans, bubble trays or the like, not illustrated; in the upper portion of chamber 80, remove a relatively hot condensate from one of the lower trays ory decks and return the same in regulated quantities and without intentional cooling to a point in chamber S6 above that from which it is removed. In

hot Washing this manner, I provide a relatively liquid for the vapors and accomplish removal of the deleterious materials therefrom without substantial cooling and reflux condensation. In the case here illustrated, directed from a suitable point in chamber 80 through line |95 and valve |05 to pump` |01 wherefrom it is returned through line |38 and valve |09 to a higher point in chamber 80. Since the closed cycle is thus estab-lished, through which heavy condensate is continuously circulated, any, required amount of washing liquid may be provided by controlling the speed of pump |91. However, prolonged continuous circulation of thismaterial will reduce its efficiency since the deleterious heavy material-s, which it removes from the vapors, will accumulate therein. I,

therefore, provide for continuously or intermit.

tently bleeding olf a portion of the washing liquid and removing the same from the system. Line H; controlled by valve is provided for this purpose, in the case here illustrated, and the relatively heavy and dirty liquid, thus removed from the system, may be discharged through line ||9 and valve to cooling and separate.

storage or it may, when desired, be blended, by well known means not illustrated, with the residual product removed from the lower portion of chamber 39,

The resulting, relatively clean vapors are directed from the upper portion of chamber 80 through line 9| and valve 92 to condensation and cooling in condenser 93 and the resulting condensate and uncondensed gases pass through line 94 and valve 95 to collection and separation in receiver 99. The condensate is removed from receiver 96 and directed through line 91l and valve 98 to storage or elsewhere, as desired. The gaseous products may be released from receiver 96 in the usual manner, by Well known means not illustrated, or' preferably, in case sub-atmospheric pressure is employed in chamber 80, they are directed from receiver 99 throughk line 99 to a vacuum pump, not illustrated, or preferably to some well known type of jet ejector such as indicated, for example, at |60, whereby sub-atmospheric pressure is maintained in receiver 96, condenser 93 and chamber 80; In the case here illustrated, steam is supplied through line lill to ejector |90 and induces the flow of gasesy from receiver 95 through line 9S to condenser |92 wherein the steam is substantially condensed, to create a sub-atmospheric pressure in this zone, by introducing cold water through line |93 and valve Idil into direct contact therewith, the condensate being discharged from condensing chamber |92' through line |93 which has a suitable trap at its lower end to prevent atmospheric air from entering chamber |62 and breaking the partial vacuum in this zone.

When relatively light refractory distillate is supplied to coil 16, as previously described, in addition to serving as a means of increasing velocity through the coil. and decreasing theeffective pressure in chamber. 8D, it serves as a blendheavy condensate is 1 ing agent for the condensate collected in receiver 96 and improves its fuel oil characteristics. By selecting a distillate for this purpose which does not: have too 10W an initial boiling point and which, due to its refractory nature, will not undergoappreciable cracking in coil 16, and by regulating' the amount of distillate so used, I am ableftourecover a; condensate in receiver 96 meetingthe, requirements for premium fuel oil. l have;` found that-selected light fractions of the intermediate liquidlproducts formed in a conventional cracking; operation, which fractions are commonly termed pressure distillate bottoms" and-'havean approximate boiling range of 400 to 600 E., or thereabouts, are particularly suitable forthepurpose and, further, that the quantity of suchmat'erial necessary for blending with the condensate ofthe residuum cracking and reducing operation, to improve its fuel oil characteristics,.wil1 give the desired results with respect to velocity and partial pressure in coil 16 and chamber 89; A considerable variation in the amount of light distillatesupplied to coil 19, so that this amount willv correspond. to that required for blending, is made possible Without defeating its other purposes, by employing compensating variations in thering conditions (and hence in the rates ofy heating) in furnace 11 and/or by varying the absolute pressure employed in chamber 80. For example, when a certain proportion of light distillate to flashed residue, in the mixture supplied to coil 16, is found to give a satisfactory degree ofA crackingfor the flashed residue, under the specific temperature and pressure conditions employed, and the distillate collected in receiver lirequires a greater quantity of light fractions to blingit to market specifications for premium fuel oil,. the quantity of` light distillate supplied to coil 15 may be ,correspondingly increased and, to compensate for this, somewhat higher rates of heating and a higher coil outlet temperature may be employed and/or the absolute pressure `employed' in chamber Sil-may be increased. No set rules have been formulated for predetermining theexactv temperature and pressure conditions and the exact proportions of flashed residue to light distillatein the mixture supplied to the flashed residue cracking and reducing step since these proportions will vary, depending upon the particular characteristics of the flashed residue being treated'which, in turn, will depend upon the nature of the cracking stock from which they are derived and the conditions under which they are produced. However, for any given cracking stock andA any' given set of operating conditions, in that portion* of thesystem preceding the flashed residue cracking and reducing steps, the proper operating conditions of the latter step may be empirically determined by starting the operation usinganexcess amount of light distillate supplied to coil 1.6, then' gradually decreasing this amount until the characteristics of the condensate collected'in receiver 96 are satisfactory andadjustingj the temperature and pressure conditions in coil 1.6and chamber to correspond. I have found, for example, that with most cracked residuessubjected to two stages of liash distillation, in the manner hereinbefore described, and with temperatures of 'the order'. of 850 to 950 F. at the outlet of. coil 1B and with an absolute pressure in chamber 80 of the order of 50 mm. of mercury up to substantially atmospheric pressure, approximately 12,to 18% of substantially gas-free pressure distillate bottoms, based on the weight of the flashed. residue.` supplied to coil 1S, will give the desired results with rates of heating, in that portion of coil 16 wherein the materials passing therethrough are at an active cracking temperature, of the order of 8,000 to 15,000 B. t. u.s per hour, per square foot of external heating surface.

It is, of course, Within the scope of the invention to supply light distillates, other than pressure distillate bottoms, to coil 16 for the purposes above mentioned. The only essential requirements of this material being that it is relatively low-boiling and readily vaporizable, will not be materially cracked under the conditions employed in the heating coil and will not contaminate the final fuel oilproduct or too greatly reduce its ash point. Other materials which are suitable for this purpose are, for example, straight-run or cracked naphtha, heavy gasoline fractions, light refractory gas oil and the like.

Provision is made for supplying either, straightrun or cracked light distillate from storage or from a separate cracking system or elsewhere to coil 16 by means of line IISand valve II 9 communicating with coil 16 through lines 84 and 15.

The invention specifically contemplates the use of the secondary ashing step vof the system and/or the flashed ,residue cracking and reducing step in conjunction with a plurality of conventional cracking units for reducing and converting the residual liquid produced within the latter. Provision is therefore made in the apparatus here illustrated for supplying residual liquid in heated state from one or a plurality of other cracking units, not illustrated, to ychamber 31 by means of line II2 and valve IIS communicating with line 33. Provision is also made for introducing any heavy residual cil amenable to treatment, in the manner described, in coil 16, directly to the latter zone from the flash distilling step of a separate cracking system or from storage or elsewhere, as desired, through line II4 and valve I I5. I have so provided for supplying a regulated portion or all of the oil removed from the lower portion of dephlegmator 40 to one or a plurality of cracking systems, other than that illustrated, through line IIS and' valve II1.

The preferred range of operating conditions which may be employed in an apparatus such as illustrated and above described to accomplish the desired results are approximately as follows: A cracking temperature of the order of 850 to 950 F., or more, may be employed at the outlet of heating coil I with a superatmospheric pressure at this point in the system of the order of 100 to 350 pounds, or more, per square inch. Substantially the same or a somewhat lower Vpressure may be employed in reaction chamber 5 and the succeeding vaporizing and separating chamber 8 may be operatedat a reduced superatmosphere pressure of the order of 50 to 150 pounds, or thereabouts, per squarev inch. The pressures employed in fractionator II and the succeeding condensing and collecting equipment Will be substantially the same or lower than that employed in chamber 8. Secondary vaporizing and separating chamber 31 is operated at a lower pressure than that employed in chamber 8, the reduced pressure ranging, for example, from 50 pounds, or thereabouts, per square inch, superatmospheric, down to substantially atmospheric pressure. Fractionator 40, condenser 55 and receiver 58 are preferably operated at substantially the same pressure as'that employed in chamber 31, although lower pressures may be utilized, when desired. The temperature employed at the series-chamber type, multiple coil cracking syssol outlet of the flashed residue heating coil 'I6 may range, for example, from 775 to 950 F., or thereabouts, and the pressure employed at ,the outlet of this coil is preferably of the order of substantially atmospheric to 30 pounds, or thereabouts, per square inch, superatmospheric pressure. The pressure employed in chamber 80 may range kfrom substantially atmospheric or a slight superatmospheric pressure down to a subatmospheric pressure corresponding to 50 mm. of mercury, or less, sub-atmospheric pressure being preferred in-this zone. The pressure employed in chamber` 80 may be substantially equalized in the succeeding condensing and collecting equipment.

As anexample of one specific operation of the residue reducing and cracking steps of the process herein disclosed, a flashed liquid residue of approximately 17 A. P. I. is withdrawn from the vaporizing and separating chamber yof a tem at a temperature of about 800 F. and supplied without intentional cooling to a secondary vaporizing and separating chamber operated at substantially atmospheric pressure. The ashed residual liquid is reduced in the secondary vaporizing and `separating chamber to a gravity of ap'- proximately 0 A. P. I. and is directed therefrom at a temperature of approximately 700 F. to the residue heating coil. The vapors evolved in the secondary vaporizing and separating chamber. are dephlegmated in contact with the charging stock for the process which is a heavy reduced crude` of approximately 14.4 A. P. I. gravity. 1 An overhead stream of dephlegmated vapors is removed from the upper portion of the dephlegmatorat approximately 400 F. and subriectedto condensation and cooling to form a distillate of about 35 A. P. I. gravity. Thismaterial amounts to about 22% by weight of the flashed residue supplied to the secondary vaporizing and separating chamber. A suiiicient quantity offthis materialv is returned to the upper portion of the secondary vaporizing and separating chamber to maintain a vapor outlet temperature `from this zone of approximately 675 F. The remaining portion of -this distillate is returned to the fractionator of the cracking system. 'Ihe mixture of condensate and preheated charging stock formed in the dephlegmating step has a gravity of approximately 13 to 14 A. P. I. It is removed from the dephlegmator and supplied to the fractionator of the cracking system.

yThe quantity. of secondary flashed residue produced is approximately 50% by weight of the flashed residue supplied to the secondary vaporizing and separating `chamber and the additional cracking stock recovered therefrom in the form of distillate and condensate, returned, as above described, tothe fractionator of the cracking system, amounts to approximately 50% by Weight. of the primary :dashed residue. The quantity of charging stock Supplied to the dephlegmator is approximately the same by Weight as the quantity of v'primary ashedresidue supplied to the secondary vaporizing and separating chamber. Therefore, in addition to the quantity of recycle stock produced inthe conventional cracking operation with one stage of flash .distillation, an additional quantity of cracking .stock amounting to nearly 50% by weight ofthe rawoil charging stock is produced in the secondary flashingstep. v

The secondary flashed residue is. blended prior vaporization Without additional heating and Without intentional cooling to said semi-solid residue, removing the latter in heated fluid state from said loW pressure Zone, separately removing vapors evolved from said heated products in the low pressure zone therefrom, and condensing the saine to form said fuel oil product.

6. The process defined in claim 5, wherein oil resulting from said condensation of the vapors evolved in the second named flash distilling step is returned to the rst mentioned fractionating step.

7. The process dened in claim 5, wherein vapors evolved in the second mentioned flash distilling step are dephlegrnated to form relatively light vapors and relatively heavy condensate, the latter vloeing returned to the cracking operation for further cracking treatment and said lower boiling dephlegmated vapors Ilceing separately condensed to form distillate which is returned, in part, to the second named flash distilling step as a cooling and reluxing medium and, `in part, to the :first mentioned fractionating step.

8. A conversion process which comprises subjecting hydrocarbon oil to cracking conditions of temperature and pressure and ilash distilling the resultant products to separate the same into vapors and unvaporized oil, fractionating the vapors to form relatively heavy and light reux ccndensates, further flashing the unvaporized oil to reduce the same to a heavy residual liquid, condensing the vapors evolved by said further flashing and returning resultant condensate to the cracking step, combining said heavy residual liquid With light reflux condensate formed by the fractionation, heating the resultant mixture in a heating coil suiiiciently to vaporize said light condensate and mildly crack the residual liquid, discharging the heated mixture into a 10W pressure vaporizing zone and therein separating the same into vapors and residue independently of the products of the rst-mentioned cracking step, and condensing and collecting the lastrnentioned vapors PERCY MATHER. 

